Phospholipids are a major component of the cellular membrane and participate in the regulation of cellular functions, act as second messengers, and as substrates for phospholipases, lipid kinases, and phosphatases. Once thought to merely house protein machinery, phospholipids are now known to participate in the regulation of cellular and sub-cellular biochemical functions such as membrane trafficking, regulating membrane proteins, and creating sub-cellular compartments which contribute to overall cellular functioning.1,2 
Nature has evolved a diverse library of phospholipids and lipidomic analyses have identified the existence of several, structurally different lipid types existing within a single cell.2 Lipid architecture is generally derived from a glycerol backbone to which several different fatty acids and phosphate head groups can be appended to generate a large library of lipids.
Phospholipids present three distinct regions where chemical modifications allow for the generation non-natural lipid molecules. The hydrophilic phosphate head group can be linked to one of several moieties such as choline, ethanolamine, glycerol, inositol, or serine. Lipid head groups have been shown to direct lipids to either the external or cytosolic leaflet of the plasma membrane.2 
Modification of the head group through tethering polyethylene glycol oligomers (PEGylation) has been used to tune the hydrophilicity of the head group and results in reducing or eliminating enzymatic hydrolysis and promotes extended circulation times of lipid nanoparticles in vivo.3 
The glycerol backbone of phospholipids presents another potential location for chemical modification. In nature, changing of the ester linkage to that of an ether (or an enyl linkage) has biological implications. For example, 1-alkylglycerophosphocholines have been implicated as anti-hypertensive agents4, and play a role as selective cytotoxic agents in some human cancer cell lines.5,6 Stereospecific methods have been developed to produce libraries of ether and thioether lipids7 as well as amide-derived lipids.8 
The fatty acid chains of lipids presents a further location in which modifications can be incorporated, for example, which tune the hydrophobic character of the lipid. The incorporation of short fluorinated segments into the fatty acid (FA) tails has been disclosed to provide higher stability and longer circulation times for lipid nanoparticles in vivo.9,10 The introduction of a single fluorine into the myristic acid 1,2-dimyristoyl-sn-3-glycerolphosphocholine (DMPC) chains was observed to not interrupt overall lipid order or the phase transition temperature.11,12 Asymmetric bolaphospholipids featuring ether linkages have been synthesized and their self-assembly behaviour studied.13 Modifications to the FA chains are commonly introduced to incorporate fluorophores enabling phospholipase kinetic experiments to be performed.14 
Krishnamohanrao et al. prepared two asymmetric phosphocholines in which one of the chains was modified with a chlorodimethylsiloxy group (Scheme 1).15

EP 0292760 reports the preparation of linear and cyclic alkylpolysiloxanes having the following general formulae I and II:
wherein each R is an alkyl radical and A is an organic group having the general formula:
wherein R1 is an alkylene group containing 3 to 50 carbon atoms, R2 is selected from hydrogen atoms and an alkyl group containing 1 to 25 carbon atoms, B is selected from the group R, hydrogen atoms and the group A, with the proviso that there is at least one A group in the molecule.
Phospholipids with long chain fatty acid tails (>10 carbons) self-assemble into multilamellar vesicles (MLVs) in aqueous solutions. Unilamellar vesicles (ULVs) differ from MLVs in that circulation times can be extended, making ULVs better suited as delivery vehicles. From a delivery perspective small ULVs, ranging in size from 50-150 nm and with low size polydispersity, are desirable. Current methods for preparing ULVs include sonication or tedious extrusion procedures which can be time consuming and require expensive specialized equipment.16 Spontaneous vesicle formation has been observed previously and vesicles formed in this manner may be useful for drug delivery.17 